Study of Polar Spikes and Polar Rays in C.H. using SXRT

qs096.koutchmy01
Posted:  26-Nov-95
Updated: 20-Jul-96
Events specified: N/A

Serge Koutchmy (NAO & Paris Inst-t Ap CNRS) in collaboration with H. Hara (NAO & Yohkoh team ISAS).

1- Purpose of the study

Identify and deduce relevant parameters of small scale features seen at high temperature in polar regions at time when polar faculae are still active. Compare with what is known from WL studies, especially those done at time of solar total eclipses. Clear up the problem of overlap of different polar structures and measure their lifetime and period of rotation.

2- Scientific Justification

Many small scale structures were observed in the past above polar regions using WL eclipse imaging: polar plumes; polar rays; spikes; macro spicules and polar surges; sheet- streamers seen edge-on and edges of high latitude streamers; arcades at the boundary of high latitude filaments; plasmoides and threads; voids and rifts; polar jets; etc. There is clearly a problem of overlap along the l.o.s. so Yohkoh observations provide a good opportunity to clear up this question thanks to the temporal coverage which is possible to acheive with the SXRT. SXRT image shows only the hot component of polar emissions. Moreover, the time resolution will be indeed limited by the need to perform long integrations. Accordingly, we propose to put a priority on the image processing of integrated sequences to identify at first the most stable features which could show some definite rotational properties and permit a stereo- view. Further, the time sequence should permit to pick up also some 'instant' phenomena beleive to correspond to high velocity impulsive events or jets. This is foundamental to understand the sources of the fast solar wind.

3- Observing procedure

a- Limit the fov to 512x128 px around the N- polar region. Take the longest exposure time compatible with the dark noise (30 sec ?). Take time series of at least 16 consecutive images or possibly more. Guiding errors are needed to post- co- aligned images. b- Observations should be repeated at least 3 to 4 consecutive days (1 to 2 times per day). c- Groundbased H alpha observations of the polar region will be collected weather permits. 4- References

on polar CH: S. Koutchmy 1977 Solar Phys. 51 pp 399- 407 
on polar coronal spikes: Koutchmy & Stellmacher 1976 SP 49 pp 253- 265 
on polar jets: S. Koutchmy & M. Loucif, 1990 in "Mechanisms of Chrom. and 
               Coronal heating" Ulmschneider et al. Ed., S.V. pp 192- 197

This is an addendum to the earlier proposal of SXT observations of Polar Spikes etc. by S. Koutchmy and H.Hara

sept.11, 1995

to attention Prof. Watanabe copies: HHu, KR, KS, YS, MW, SK, HHa

Observations done last sept.2 1995 were quite successfull. A new phenomenon, relevant to the physics of CH and quiet Sun, is probably discovered. Several scientists are now taking part in this research. Beside H.Hara and me and without any order of priority, K. Shibata, K. Reardon, M. Weber, Y. Suematsu, H. Hudson and may be more in the future...(from ground-based supporting observations). There is still possible improvement to make on the procedure used to observe from Yohkoh SXRT. We could improve the sampling rate, by reducing with a factor 2 the fov, namely reduce the height of partial frames (take half) making sure that we have the N-pole slightly higher (leaving just 1/4 of the sky above the pole inside the fov) than the center of the frames. An other improvement would be taking calibration frames of the dark noise and possibly, of the Earth (stray light). Having more groundbased support is also an issue so it would be efficient to let us know as soon as possible when a new run is planned on this program. As far as the exposure time is concerned it seems that 30 sec is an optimum number on SXRT.

The sept. 2, 1995 run has been processed at ISAS and at Mitaka; preliminary results are deduced. A paper will be prepared soon by SK in collaboration with all the co-Is.

Peliminary title: 'SXR Jets observed in a Polar CH'

to be submitted to PASJ (with 1 or 2 colored images)

potential co-Authors: S. Koutchmy, K. Shibata; K. Reardon; H. Hara; Y. Suematsu; M. Weber; H. Hudson; ...?

Abstract (preliminary): Following a successful run of specially focussed observations made to detect SXR impulsive events in a polar coronal hole, we report the detection of a new Yohkoh discovery we name SXR polar jets. SXRT observations of sept.2, 1995, performed at an average rate of 45 sec during

several hours, above the N- pole CH, are reported. 
A movie was assembled from 200 images to allow the evaluation of dynamical 
events: polar transient brightenings and recurrent point-like SXR bursts. 
High speed jets are well detected during the impulsive phase of the brightest

SXR brightenings originating from the CH. Jets extend over the whole fov almost strictly in a radial direction. Proper motion corresponds to a speed of 500 km/sec. A large distersion of the energetic signature of all events is noticed, suggesting a rather flat spectral energy distribution with sizes. Theoretical interpretation of jets should imply magnetic anihilation processes and we argue in favor of a model which could possibly unify more observations taken at groundbase and in space. The obvious implications for the origine of the fast wind and mass loss in CH is noticed.

Update 20-Jul-96

1- A preliminary evaluation of the sept.2, 1995 run was made at ISAS in sept/oct. 96. A movie was assembled by K. Reardon; short time series were discussed by K. Shibata and others at Mitaka. The outline of a preliminary paper to be submitted to PASJ was proposed. We found it necessary to come back to the individual images of each time series in order to perform a more quantitative analysis of identified events. This was done by producing a set of 'posters' with images in negative to better reproduce low intensity single px brightenings and weak events (jan/feb. 96).

2- A new run was performed during the total solar eclipse of oct. 24, 1995. Polar plumes and rays were very well recorded at ground-based above polar regions, using W-L imaging with radial filter, in India and in Viet- Nam. It makes evident the need for considering the relationships between polar WL plumes and SXR polar jets and jetlets.

3- The successful launch of the SOHO mission and the not less successful operations with the EIT exp-t (since feb. 96) is a great step in the study of energetic events in polar regions which cannot be ignored in the context of our analysis. Several collaborative works were started on Polar Plumes. Without going into the details, we evaluated the observed with EIT coronal-channels (Fe IX to XV) EUV polar plumes which look not exactly similar to our SXR jetlets. They seem to be different components of a larger scale and more stationary phenomenon related to the W-L polar plumes which extend far away in the corona and may be in the interplanetary space. This question has to be considered if not elucidated, at least superficially, to properly interpret what we discovered with the SXT.

4- From the examination of the available EIT movies taken above polar regions, we concluded that: a- The 30.4 nm HeII small scale limb events are similar to Halpha large spicules (macro- spicules); b- The plumes (jets ?) seen in Fe IX/ XV have a long lifetime and we cannot recognize the very large variabilities seen in SXR. It is not clear if this is due to the undersampling of EIT observations or if this is a real behavior. EUV plumes are more like W-L plumes: they are present all the time. c- It is difficult to distinguish the behavior of EUV plumes coming from the inside part of the polar CH and those coming from the edge. We conclude that SXR jetlets are different.

5- A more carefull examination of the frame-to-frame SXT images did reveal some new properties appearing as quasi- single px brightenings. A special analysis was performed including the time series which was obtained on aug. 25, 1995 with a shorter (15 sec) exposure time. We are comparing this finding with the results of Shimizu (1995) which concern far more energetic events occuring in active regions. We think that our very short and quasi- single px brightenings are more likely the SXR counterparts of the Porter et al (1984) UV brightenings that we observed in polar regions... A planned short paper describing this finding is in preparation.

IN CONCLUSION, we think that the sept. 95 run on the N- polar region still fully justify the rapid submission of a paper to PASJ and we want to continue this collaboration at least until the printing of the 2 planned papers.